Traditionally, AuGeNi ohmic contacts are used for GaAs based FETs and HEMTs. This requires annealing the device after contacts to temperatures greater than 300-400.degree. C. Non-alloyed ohmic contacts to gallium arsenide (GaAs) have been demonstrated in the past by growing indium gallium arsenide (InGaAs) on GaAs and utilizing the contact to indium arsenide (InAs) to achieve low resistance. In the past the only way to achieve low contact resistance has been to grade the contact layer with In.sub.( 1-x) Ga.sub.x As, where X varies from 1 to 0, i.e. the layer varies from GaAs to InAs. The problem is that this graded growth introduces substantial complexity in the growth process and is not suitable for selectively grown contacts.
Accordingly, it would be highly desirable to provide improved fabrication methods for ohmic contacts.
It is a purpose of the present invention to provide improved fabrication methods for multi-layer heterostructures.
It is another purpose of the present invention to decrease contact resistance in a multi-layer heterostructure.
It is still another purpose of the present invention to provide a new and improved method of providing continuity at a crystalline/substrate interface of an ohmic contact.
It is a further purpose of the present invention to provide a new and improved fabrication method for non-alloyed ohmic contacts.